A phase controller may control current flowing through a switching device that is switched on and off according to a pulse signal output from a pulse width modulation (PWM) circuit. In the case where the outputs of PWM circuits of a plurality of channels are controlled with the same power supply in such a phase controller, if the pulse signals output from the respective PWM circuits change simultaneously, switching may noise occur, and cause a disturbance in waveform or a large fluctuation in power supply.
One technique to avoid switching noise is to prevent the pulse signals of the respective channels from changing simultaneously (colliding). A conceivable method for avoiding such edge collision of pulse signals is to add a fixed phase difference between the signals of the respective channels. However, in the case of feedback-controlling each PWM circuit, the pulse width from an on edge to an off edge changes dynamically. Accordingly, even when the fixed phase difference is provided between the channels to avoid a collision between on edges, it is difficult to avoid a collision between an on edge and an off edge and a collision between off edges. Particularly in the case where the pulse width is updated in a short unit such as several hundred Hz or less, collision avoidance computation needs to be performed in a time shorter than the unit.
In the drawings, like reference numbers generally indicate identical or similar elements. Additionally, generally, the left-most digit(s) of a reference number identifies the drawing in which the reference number first appears.